1. Field of the Invention
The present invention relates to a tuyere for use in refining molten metals; more particularly, to a tuyere whose flow passage for refining gas is configured to provide in transverse section a greater perimeter than a circular flow passage of corresponding area.
2. Description of the Prior Art
The refining of molten pig iron into steel in a bottom-blown steelmaking converter is well-known. Generally, the refining process involves the use of concentric tube tuyeres embedded in the converter beneath the surface of the molten metal bath; the concentric tubes usually have a constant thickness and are of circular cross section. An oxidizing gas, usually pure oxygen, is blown into the bath through the central (inner) tube of each tuyere and a protective fluid is blown through the annulus formed by the inner and outer tubes of each tuyere to prevent undue wear of the tuyere tip. U.S. Pat. No. 3,817,744 discusses such a refining process in detail.
One of the problems that confronts steelmakers is the determination of the optimum number of tuyeres to be used in a converter of given size. If the number of tuyeres is large, the technical problems surrounding the introduction of fluids into the tuyeres and the control of their respective flow rates are complex. Thus, generally it is desirable to utilize the minimum number of tuyeres. But, if a small number of tuyeres are selected, the cross-sectional area of the passage used for oxidizing gas in each tuyere must be relatively large to maintain the desired blowing period and, in the case of a passage of circular cross section, this means a passage of relatively large diameter.
The use of large diameter oxygen flow passages in a bottom blown refining process can result in a number of process disadvantages such as the throwing-up (e.g. slopping, spitting) of metal and/or slag from the bath with a consequent formation of skulls around the interior of the converter mouth, and an inadequate distribution of oxidizing gas within the metal bath. These disadvantages manifest themselves in slags with unduly high iron contents, the production of reddish-brown smoke, high oxygen consumption, etc.
U.S. Pat. No. 3,802,684 addresses to some extent the problem of "spitting" in bottom blown steelmaking processes as caused by large diameter circular flow passages in the tuyeres. The solution put forth in that patent is to provide an inner tube having a noncircular oblong transverse cross section and an outer tube of the same shape.